The product characteristics of bimodal resin systems, that is resin products that are produced by more than one catalyst system, are dependent of the distribution of the molecular species. Where more than one catalyst and one or more monomer(s) are used to produce a polymeric product (e.g. the product being a mixture of different homopolymers/and co- or terpolymers) precise control of the multiple polymerization reactions in the reactor is required for repeatability in producing products. The need for reactor control is traditionally met by periodically analyzing the reaction product. In the production of bimodal resin systems, for example, this is most often done by analyzing the polymer product at some point in time after the material has been produced. But this practice suffers from the disadvantage that such a measurement is a cumulative reactor split, that is, a time average of the product produced as sampled from a reactor. Further, while the analytical approach for obtaining actual split data may be performed using different analytical techniques, for example GPC or SEC (gel permeation or size exclusion molar mass or molecular weight measurements), they are highly dependent on resin sampling, sample preparation, the generation of the data and the reduction of the data into an estimate of the fraction of each polymer in the product (e.g. SEC data must be deconvoluted and the individual molecular weight distributions estimated). Because the time required to determine reactor split using this process may be several hours (between the actual polymerization and the analysis of split), the data may be of little or no utility even when the sampling, measurement and data interpretation is accurate and precise. Additionally, the SEC (size exclusion chromatography) measurement is fairly cost intensive and prone to error and as such somewhat inadequate for process control, especially continuous process control. Accordingly, there is a need for improvements in mixed catalyst continuous polymerization process control. The present invention provides some solutions to this problem.